The USS Wahoo (SS-238) was a Gato class submarine. The Gatos,
and their successors, the Balao and Tench class subs, formed the vast
majority of the U. S. Submarines in the second world war. The Balaos were
essentially the same as the Gatos; the major difference between the two
was the Balao's improved pressure hull that permitted greater depths.

The diagram below is of a typical Gato/Balao class sub. The photos were
taken of the USS Bowfin (SS-287) in April, 2000. The Bowfin, is a
Balao class sub and is on display at Pearl Harbor.